1. Field of the Invention
The present invention relates to fluidising apparatus.
2. Description of the Related Art
Fluidisers are known for hydraulic conveyance of loose materials. A typical application of fluidisers is the removal of sand from a vessel. Sand at the base of the vessel tends to be packed substantially solid and is therefore difficult to move. A fluidising apparatus disclosed in U.S. Pat. No. 4,978,251 works by discharging a liquid under pressure into a sand containing vessel. The pressurised liquid emerges in a downward annular flow which creates a vortex within an adjacent region of the vessel (known as the “radius of influence”). The liquid mixes with the sand and fluidises it to form a slurry. The slurry can then enter a discharge pipe for conveyance to a remote location.
Unfortunately, there are several problems associated with such conventional fluidisers. First, such fluidisers are fitted inside the vessel. This makes maintenance access difficult and can interfere with other internal components inside the vessel. Furthermore, the pipes supplying the pressurised liquid and the pipe discharging the slurry are arranged so that they are concentric along a significant portion of their lengths. Therefore, if one of the pipes is damaged or becomes blocked then a significant amount of work and disruption is involved in fixing the problem. The swirling water emerging from the discharge pipe is also at risk of returning into the device. Another disadvantage is that the “radius of influence” of conventional fluidisers is relatively limited in directions radial to the water supply pipe. Conventional fluidisers require two pipes to penetrate the vessel and mate up to it, and these can be difficult to fit.
U.S. Pat. No. 5,637,278 discloses a fluidiser of a similar design to that of U.S. Pat. No. 4,978,251, but protruding upwards into the base of a vessel. When such apparatus is being used in a vessel in which gravity separation of oil and water is taking place, the vortex it creates causes a disturbance that extends a considerable distance into the vessel. This can disturb the gravity separation and the water and the oil may become mixed together again. The vortex can also draw oil into the apparatus so that oil is discharged in the slurry. If this happens then the oil will usually have to be separated from the slurry to avoid pollution and monetary loss.
U.S. Pat. No. 3,178,233 shows a fluidising arrangement for a chamber including an inlet pipe which is concentric with and surrounding an outlet duct. A bonnet can be connected so that the inlet jets are located beneath the lower surface of the deflector. GB 1348042 shows an apparatus having a rotatable cylindrical inlet duct with a single nozzle at its upper end. Detection rods are used to determine the level of material in the tank and feedback from the detectors are used to control the speed of rotation.